Propeller blade testing apparatus



May 22, 1956 R. c. TRESEDER PROPELLER BLADE TESTING APPARATUS 2Sheets-Sheet 1 Filed Aug. 2, 1952 INVENTOR. P051527 C. TQESEDEQATTORNEYS May 22, 1956 c. TRESEDER 2,746,290

PROPELLER BLADE TESTING APPARATUS Filed Aug. 2, 1952 2 Sheets-Sheet 2Moro/a INVENTOR. ROBERT C, 7725552752 %2 ATTORNEYS United States PatentC PROPELLER BLADE TESTING APPARATUS Robert C. Treseder, Dayton, Ohio,assiguor to General Motors Corporation, Detroit, Mich., a corporation ofDelaware Application August 2, 1952, Serial No. 302,321

7 Claims. (Cl. 73-147) The present invention relates to testingapparatus and more particularly to apparatus for ascertaining thestructural characteristics of propeller blades.

Existing apparatus for determining the structural characteristics ofpropeller blades is inadequate. Modern practice dictates the necessityfor providing test apparatus to obtain the requisite data on bladestrength by closely approximating or duplicating flight propeller load,-ings in the laboratory. The present invention provides means forinducing flatwise vibratory stresses in propeller blades by torsionalexcitation, which stresses are normally encountered in flight due to theangle of air inflow to a propeller unit. Thus, the ability of a blade towithstand flight stresses can be accurately predicted by simulatingflight loadings in the laboratory. Accordingly, amon my objects are theprovision of a means for stressing propeller blades through vibratoryexcitation to determine the structural characteristics thereof.

The aforementioned and other objects are accomplished in the presentinvention by providing means for producing llatwise vibratory stressesin propeller blades by cyclically altering the pitch setting of theblades of a rotating propeller unit. Specifically, the apparatusincludes a rotatable propeller hub having a plurality of sockets adaptedto support propeller blades for movement about their longitudinal axes.Associated with each of the hub sockets is a pitch changing torque unitincluding positive stops for determining the range of cyclic pitchchange movement. The torque units are actuated by hydraulic fluid mediumunder pressure, which is supplied thereto through a stationary pineapplehaving passages for the flow of fluid medium to and from the torqueunits under the control of a pitch cycling valve. The pitch cyclingvalve is actuated by a suitable motor and controls the flow of fluid toand from the hub torque units to cyclically alter the pitch position ofthe propeller blades under test. Fluid under pressure is produced by apump having connection with a reservoir and with the sup ly port of thevalve. The blades may be instrumented with strain gages to determine themagnitude of the stresses produced therein.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

In the drawings:

Fig. l is a viewin perspective of apparatus constructed according to thepresent invention.

Fig. 2 is a view partly in section and partly diagrammatic illustratingthe principle of operation.

Referring more particularly to Fig. l, the present invention isexemplified in conjunction to a propeller unit including a universal hub10 having a plurality of radially extending sockets 13., which areadapted to receive a plurality of blades 12. The blades 12 are journaledfor rotation about their longitudinal axes within the hub sockets 11 ina manner to be later described. The hub 10 is suitably supported and isadapted to be rotated by means of a motor 13. The hub 10 is furtherprovided with a central through bore within which a stationary pineapple14 is disposed. The stationary pineapple is connected by tubing 15 and16 to the outlet ports of a four-way cycling valve unit 17. The cyclingvalve unit 17 is operated by an electric motor 18 having connectiontherewith through a crank mechanism 19 and a connecting rod 21'). Fluidmedium under pressure is supplied to the supply port of the cyclingvalve unit 17 through tubing 21.

As previously mentioned, it is desirable to demonstrate the ability ofpropeller blades to withstand the stresses normally encountered inflight before the blades are installed on an aircraft. Existing testapparatus is inadequate in that flight loadings cannot be duplicated oreven closely approximated. Furthermore, existing test apparatus producesextraneous stresses, which sometimes cause failure of the blades beforethe design flatwise vibratory bending stresses have been reached. Theability of a propeller blade to withstand fiatwise vibratory bendingstresses is indicative of the structural integrity of a propeller blade.Flatwise vibratory loads on propeller blades occur in flight when theair stream enters the, propeller unit at an angle other than Thisphenomenon produces a flatwise bend cycle in each blade every revolutionof the propeller unit due to sinusoidally varying aerodynamic loading.Accordingly, this phenomenon, which is known as a 1P bend, is animportant criteria in the desi n of a propeller blade. The presentinvention provides a method and apparatus of simulating flight loadingsof this character in the laboratory.

The fiatwise bending is induced in propeller blades by cycling the pitchsetting thereof in a predetermined relation to the rotational speed ofthe test unit. in other words, the fiatwise bending is effected byexciting the blade torsionally. If the pitch is cycled once perrevolution of the test unit hub, the stresses encountered by a 1? bendin flight may be closely approximated. The present invention providesmeans for obtaining this result, but has versatility in that therotating blade may be excited at any desirable frequency with respect tothe rotational speed thereof.

Referring more particularly to Fig. 2, the detail construction of theuniversal hub 10 and the principle of operation will be described ingreater detail. The hub ii is provided with a flange 22 to which themeans for rotating the hub may be attached. The hub is provided with acentral bore 23 Within which a portion of the stationary pineapple 1 ismounted. Disposed within the socket 1.. is an adapter 24 having a socketportion 2%? adapted to receive and rotatably journal the root end of apropeller blade 12. The adapter 24 is merely provided to accommodate thevarious sizes of blades now produced. The blade 12 is supported withinthe, adapter socket 25 by means of the conventional stacked bearings 26and bearing retaining nut assemblies 27 and 28. As shown, the blade isspline connected by means of an indexing ring 29 to a central upstandingportion 30 of the adapter 24. The adapter 24 is likewise journaled forrotation by means of stack bearings 31 Within the hub socket 11. Radialbearing means 32 are also provided between the adapter 24 and the hub10.

Centrally disposed within the hub socket 11 is an upstanding integralportion of a hub 33 having a helically splined periphery 34. Coaxiallydisposed within the hub socket 11 is a piston 35 having an axiallyextending skirt 36 provided with helical splines 37 and 38 on itsv innerand outer peripheries, respectively. Helical splines 37 mate withhelical splines 34 on the portion 33, and helical splines 38 mate withhelical splines 39 formed on a ring 40, which is attached to the adapter24 by means of a dowel pin 41. The piston forms part of a torque unit,the cylinder of which is formed by complementary portions of the hub 10and the adapter 24. The torque unit is similar in construction andoperation to the torque units disclosed in the Blanchard et a1. Patent2,307,101. One torque unit chamber 42 is connected by a transfer tube 43formed integral with the hub 10 to an annular groove 44 circumscribingthe central bore 23. The other torque unit chamber 45 is connected bymeans of a passage 46 to a second annular groove 47 likewisecircumscribing the central bore 23. The stationary pineapple portionextending into the central bore 23 of the hub is provided with a pair ofpassages 48 and 49 having communication with ports 50 and 51,respectively. The ports 50 and 51 communicate, respectively, withannular grooves 44 and 47, which circumscribe the central bore 23 of thehub.

The passages 43 and 49 of the stationary pineapple 14 are shown asdiagrammatically connected by means of lines 52 and 53 to the outletports 54 and 55 of the four-way cycling valve unit 17. The four-Waycycling valve unit 17 includes a housing 56 having a supply port 57, theoutlet ports 54 and 55 and a pair of drain ports 58 and 59. Disposedwithin the housing 56 is a plunger 60 having a pair of spaced lands 61and 62 which cooperate with ports 55 and 54, respectively. A rod portion63 of the plunger 60 extends through one end of the housing 56 and isconnected by means of the connecting rod 20 to the crank mechanism 19,which is operatively connected with the motor 18. Fluid medium underpressure is developed by a pump 64 having connection with a reservoir65.

As is readily apparent, rotation of the crank mechanism 19 by the motor18 Will effect a reciprocal movement of the plunger 60, therebyperiodically connecting the lines 52 and 53 to the supply port 57 andtodrain. In this manner fluid medium is periodically supplied to anddrained from the torque unit chambers 4-2 and 45 whereupon the piston 35will be reciprocated. Movement of the piston 35 is limited by engagementthereof with the portions of the hub 10 and the adapter 24, which definethe torque unit cylinder. Reciprocal movement of the piston 35 isconverted into rotary movement of the blade 12 through the medium of thehelical splines 34, 37, 38 and 39. As the piston moves inwardly oroutwardly with respect to the hub portion 33, a twisting or rotationoccurs between splines 34 and 37. The movement of the piston skirt36.also effects relative movement between spline teeth 38. and 39,thereby causing a rotating movement of the adapter 24, which rotation isthe sum of that caused by spline teeth 34, 37, 38 and 39. This rotarymovement is transmitted by means of the indexing ring 29 to the blade 12in a manner similar to that described in the aforementioned Blanchard etal. patent. The cyclic pitch changing movement of the blades may, forexample, be on the order of 6.

In operation the test engineer will energize motor 13 to rotate thepropeller hub 10 at any desired rotational speed. Thereafter, the motor18 will be energized and the pump 64 will be set into operationwhereupon the pitch setting of the propeller blade 12 will be cycledthroughout a predetermined range of movement as determined by thepositive stops within the torque unit. In this manner flatwiselaboratory stresses may be produced in the propeller blades, themagnitude of which may be measured by any suitable means, not shown,such as strain gages. If the test engineer desires to ascertain thestresses induced in the blades by a 1P bend, he need only adjust thespeed of the motor 18 so that the pitch of the blades 12 is cycled onceper revolution of the hub 10. However, the apparatus is extremelyversatile as the R. P. M. of the hub, the cyclic frequency and thecyclic 0d of cyclic pitch changing is of considerable utility in thatthe vibratory aerodynamic loadings normally encountered in flight may bemore nearly duplicated. In addition the possibility of creatingextraneous stresses which often result in premature blade failure issubstantially eliminated. Accordingly, the structural characteristics ofa propeller blade and its ability to withstand stresses in flight may beaccurately ascertained.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. Apparatus for inducing flatwise vibratory stresses in a propellerblade including, a hub having means for supporting a propeller blade formovement about its longitudinal axis, means disposed within said hub andoperatively connected with said blade for moving the same about itslongitudinal axis to alter the pitch setting thereof, means for rotatingsaid hub, and means for cyclically altering the pitch setting of saidpropeller blade throughout a predetermined angle and in a predeterminedrelation to the rotational speed of said hub whereby flatwise bends areproduced therein.

2. Apparatus for inducing flatwise vibratory stresses in propellerblades including, a hub having a plurality of sockets for supportingpropeller blades for movement about their longitudinal axes, fluidpressure actuated means disposed within said hub and operativelyconnected with said blades for moving the same about their longitudinalaxes to alter the pitch setting thereof, means for rotating said hub,and means for cyclically actuating the fluid pressure actuated meanswhereby flatwise bends are produced in said blades.

3. Apparatus for simulating flight stresses in propeller bladesincluding, a hub having means for supporting a plurality of propellerblades for movement about their longitudinal axes, fluid pressureactuated means disposed within said hub and operatively connected withsaid blades for moving the same about their longitudinal axes to alterthe pitch setting thereof, means for rotating said hub, and a fluidpressure system for cyclically actuating said fluid pressure actuatedmeans whereby flight stresses are simulated by cycling the pitch settingof the blades during rotation of the hub. V

4. The combination set forth in claim 3 wherein the fluid pressuresystem includes a pump and a valve in circuit connection between saidpump and said fluid pressure actuated means, and means for actuatingsaid valve independent of the rotation of said hub to produce cyclicalchanges in the pitch setting of said blades.

5. Apparatus for testing a propeller blade comprising in combination, ahub having means for supporting a propeller blade for movement about itslongitudinal axis, a fluid pressure operated torque unit disposed withinsaid hub and operatively connected to said blade for rotating the sameabout its longitudinal axis to alter the pitch position thereof, saidtorque unit comprising a cylinder having disposed therein a reciprocablepiston capable of pitch change angle may all be varied to suit theparticular exigencies of the moment. The production of vibratory bladestresses by the methfluid pressure actuation in either direction, andmeans for converting reciprocative movements of the piston into rotarymovement of said blade, means for rotating said hub, and means forcyclically actuating said torque unit so as to cyclically alter thepitch position of said blade throughout a predetermined angle and in apredetermined relation to the rotational speed of said hub wherebyflatwise vibratory stresses are produced in said propeller blade.

6. Apparatus for testing a propeller blade comprising in combination, ahub having means for supporting a propeller blade for movement about itslongitudinal axis, a fluid pressure operated torque unit disposed withinsaid hub and operatively connected to said blade for rotating the sameabout its longitudinal axis to alter the pitch position thereof, saidtorque unit comprising a cylinder having disposed therein a reciprocablepiston capable of fluid pressure actuation in either direction, means toimpart rotation to said blade upon reciprocation of said piston, andmechanical stop means limiting piston movement in both directions, meansfor rotating said hub and means for cyclically actuating said torqueunit so as to cyclically alter the pitch position of said bladethroughout a predetermined angle and in a predetermined relation to therotational speed of said hub whereby flatwise bends are produced in saidblade.

7. The combination set forth in claim 5 wherein the last recited meanscomprises a fluid pressure system including, a source of fluid pressureand valve means interconnecting the source of fluid pressure and saidtorque unit, and wherein said apparatus includes means for cyclicallyactuating the valve means to efiect cyclic alteration of the pitchposition of said propeller blade.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES War Dept. Technical Manual, Aircraft Propellers, TM 1-412,January 5, 1944, pp. 125-135.

